Display screen or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of a first image of a display screen or portionthereof with a transitional graphical user interface showing our newdesign;

FIG. 2 is a front view thereof, depicting a second image of thetransitional graphical user interface.

FIG. 3 is a front view thereof, depicting a third image of thetransitional graphical user interface.

FIG. 4 is a front view thereof, depicting a fourth image of thetransitional graphical user interface.

FIG. 5 is a front view thereof, depicting a fifth image of thetransitional graphical user interface.

FIG. 6 is a front view thereof, depicting a sixth image of thetransitional graphical user interface.

FIG. 7 is a front view thereof, depicting a seventh image of thetransitional graphical user interface.

FIG. 8 is a front view thereof, depicting an eighth image of thetransitional graphical user interface.

FIG. 9 is a front view thereof, depicting a ninth image of thetransitional graphical user interface; and,

FIG. 10 is a front view thereof, depicting a tenth image of thetransitional graphical user interface.

The appearance of the transitional graphical user interface sequentiallytransitions between the images shown in FIGS. 1-10. The process orperiod in which one image transitions to another image forms no part ofthe claimed design.

The broken line showing of the display screen forms no part of theclaimed design.

CLAIM The ornamental design for a display screen or portion thereof witha transitional graphical user interface, as shown and described.